At 165,250,000 square kilometers (63,800,000 square miles) in area (as defined with an Antarctic southern border), this largest division of the World Ocean—and, in turn, the hydrosphere—covers about 46% of Earth's water surface and about one-third of its total surface area, making it larger than all of Earth's land area combined.[10] Both the center of the Water Hemisphere and the Western Hemisphere are in the Pacific Ocean. The equator subdivides it into the North Pacific Ocean and South Pacific Ocean, with two exceptions: the Galápagos and Gilbert Islands, while straddling the equator, are deemed wholly within the South Pacific.[85] Its mean depth is 4,280 meters (14,040 feet). The Mariana Trench in the western North Pacific is the deepest point in the world, reaching a depth of 10,911 meters (35,797 feet).[4] The western Pacific has many peripheral seas.

Though the peoples of Asia and Oceania have traveled the Pacific Ocean since prehistoric times, the eastern Pacific was first sighted by Europeans in the early 16th century when Spanish explorer Vasco Núñez de Balboa crossed the Isthmus of Panama in 1513 and discovered the great "southern sea" which he named Mar del Sur (in Spanish). The ocean's current name was coined by Portuguese explorer Ferdinand Magellan during the Spanish circumnavigation of the world in 1521, as he encountered favorable winds on reaching the ocean. He called it Mar Pacífico, which in both Portuguese and Spanish means "peaceful sea".[16]

History

Early migrations

Made in 1529, the Diogo Ribeiro map was the first to show the Pacific at about its proper size

Long-distance trade developed all along the coast from Mozambique to Japan. Trade, and therefore knowledge, extended to the Indonesian islands but apparently not Australia. By at least 878 when there was a significant Islamic settlement in Canton much of this trade was controlled by Arabs or Muslims. In 219 BC Xu Fu sailed out into the Pacific searching for the elixir of immortality. From 1404 to 1433 Zheng He led expeditions into the Indian Ocean.

The east side of the ocean was discovered by Spanish explorer Vasco Núñez de Balboa in 1513 after his expedition crossed the Isthmus of Panama and reached a new ocean.[8] He named it Mar del Sur (literally, "Sea of the South" or "South Sea") because the ocean was to the south of the coast of the isthmus where he first observed the Pacific.

Later, Portuguese explorer Ferdinand Magellan sailed the Pacific East to West on a Castilian (Spanish) expedition of world circumnavigation starting in 1519. Magellan called the ocean Pacífico (or "Pacific" meaning, "peaceful") because, after sailing through the stormy seas off Cape Horn, the expedition found calm waters. The ocean was often called the Sea of Magellan in his honor until the eighteenth century. Although Magellan himself died in the Philippines in 1521, Spanish Basque navigator Juan Sebastián Elcano led the expedition back to Spain across the Indian Ocean and round the Cape of Good Hope, completing the first world circumnavigation in a single expedition in 1522.[9] Sailing around and east of the Moluccas, between 1525 and 1527, Portuguese expeditions discovered the Caroline Islands,[13] the Aru Islands,[86] and Papua New Guinea.[11] In 1542–43 the Portuguese also reached Japan.[12]

In the 16th and 17th century Spain considered the Pacific Ocean a Mare clausum—a sea closed to other naval powers. As the only known entrance from the Atlantic the Strait of Magellan was at times patrolled by fleets sent to prevent entrance of non-Spanish ships. On the western end of the Pacific Ocean the Dutch threatened the Spanish Philippines.[87]

In Oceania, France got a leading position as imperial power after making Tahiti and New Caledonia protectorates in 1842 and 1853 respectively. After navy visits to Easter Island in 1875 and 1887, Chilean navy officer Policarpo Toro managed to negotiate an incorporation of the island into Chile with native Rapanui in 1888. By occupying Easter Island, Chile joined the imperial nations.(p53) By 1900 nearly all Pacific islands were in control of Britain, France, United States, Germany, Japan, and Chile.

Although the United States gained control of Guam and the Philippines from Spain in 1898,[17] Japan controlled most of the western Pacific by 1914 and occupied many other islands during World War II. However, by the end of that war, Japan was defeated and the U.S. Pacific Fleet was the virtual master of the ocean. Since the end of World War II, many former colonies in the Pacific have become independent states.

Geography

Map of the Pacific Ocean during European Exploration, circa 1754.

The Pacific separates Asia and Australia from the Americas. It may be further subdivided by the equator into northern (North Pacific) and southern (South Pacific) portions. It extends from the Antarctic region in the South to the Arctic in the north.[10] The Pacific Ocean encompasses approximately one-third of the Earth's surface, having an area of 165,200,000 km2 (63,800,000 sq mi)—significantly larger than Earth's entire landmass of some 150,000,000 km2 (58,000,000 sq mi).[18]

Extending approximately 15,500 km (9,600 mi) from the Bering Sea in the Arctic to the northern extent of the circumpolar Southern Ocean at 60°S (older definitions extend it to Antarctica's Ross Sea), the Pacific reaches its greatest east-west width at about 5°N latitude, where it stretches approximately 19,800 km (12,300 mi) from Indonesia to the coast of Colombia—halfway around the world, and more than five times the diameter of the Moon.[19] The lowest known point on Earth—the Mariana Trench—lies 10,911 m (35,797 ft; 5,966 fathoms) below sea level. Its average depth is 4,280 m (14,040 ft; 2,340 fathoms), putting the total water volume at roughly 710,000,000 km3 (170,000,000 cu mi).[10]

Due to the effects of plate tectonics, the Pacific Ocean is currently shrinking by roughly 2.5 cm (1 in) per year on three sides, roughly averaging 0.52 km2 (0.20 sq mi) a year. By contrast, the Atlantic Ocean is increasing in size.[20][21]

The Martin Waldseemüller map of 1507 was the first to show the Americas separating two distinct oceans.[4] Later, the Diogo Ribeiro map of 1529 was the first to show the Pacific at about its proper size.[4]

Islands in the Pacific Ocean are of four basic types: continental islands, high islands, coral reefs and uplifted coral platforms. Continental islands lie outside the andesite line and include New Guinea, the islands of New Zealand, and the Philippines. Some of these islands are structurally associated with nearby continents. High islands are of volcanic origin, and many contain active volcanoes. Among these are Bougainville, Hawaii, and the Solomon Islands.[32]

The coral reefs of the South Pacific are low-lying structures that have built up on basaltic lava flows under the ocean's surface. One of the most dramatic is the Great Barrier Reef off northeastern Australia with chains of reef patches. A second island type formed of coral is the uplifted coral platform, which is usually slightly larger than the low coral islands. Examples include Banaba (formerly Ocean Island) and Makatea in the Tuamotu group of French Polynesia.[16][16]

Water characteristics

The volume of the Pacific Ocean, representing about 50.1 percent of the world's oceanic water, has been estimated at some 714 million cubic kilometers (171 million cubic miles).[16] Surface water temperatures in the Pacific can vary from −1.4 °C (29.5 °F), the freezing point of sea water, in the poleward areas to about 30 °C (86 °F) near the equator.[36]Salinity also varies latitudinally, reaching a maximum of 37 parts per thousand in the southeastern area. The water near the equator, which can have a salinity as low as 34 parts per thousand, is less salty than that found in the mid-latitudes because of abundant equatorial precipitation throughout the year. The lowest counts of less than 32 parts per thousand are found in the far north as less evaporation of seawater takes place in these frigid areas.[16] The motion of Pacific waters is generally clockwise in the Northern Hemisphere (the North Pacific gyre) and counter-clockwise in the Southern Hemisphere. The North Equatorial Current, driven westward along latitude 15°N by the trade winds, turns north near the Philippines to become the warm Japan or Kuroshio Current.[4]

Turning eastward at about 45°N, the Kuroshio forks and some water moves northward as the Aleutian Current, while the rest turns southward to rejoin the North Equatorial Current.[4] The Aleutian Current branches as it approaches North America and forms the base of a counter-clockwise circulation in the Bering Sea. Its southern arm becomes the chilled slow, south-flowing California Current.[4] The South Equatorial Current, flowing west along the equator, swings southward east of New Guinea, turns east at about 50°S, and joins the main westerly circulation of the South Pacific, which includes the Earth-circling Antarctic Circumpolar Current. As it approaches the Chilean coast, the South Equatorial Current divides; one branch flows around Cape Horn and the other turns north to form the Peru or Humboldt Current.[4]

Climate

The climate patterns of the Northern and Southern Hemispheres generally mirror each other. The trade winds in the southern and eastern Pacific are remarkably steady while conditions in the North Pacific are far more varied with, for example, cold winter temperatures on the east coast of Russia contrasting with the milder weather off British Columbia during the winter months due to the preferred flow of ocean currents.[4]

In the tropical and subtropical Pacific, the El Niño Southern Oscillation (ENSO) affects weather conditions. To determine the phase of ENSO, the most recent three-month sea surface temperature average for the area approximately 3,000 km (1,900 mi) to the southeast of Hawaii is computed, and if the region is more than 0.5 °C (0.9 °F) above or below normal for that period, then an El Niño or La Niña is considered in progress.[4]

In the tropical western Pacific, the monsoon and the related wet season during the summer months contrast with dry winds in the winter which blow over the ocean from the Asian landmass.[4] Worldwide, tropical cyclone activity peaks in late summer, when the difference between temperatures aloft and sea surface temperatures is the greatest. However, each particular basin has its own seasonal patterns. On a worldwide scale, May is the least active month, while September is the most active month. November is the only month in which all the tropical cyclone basins are active.[22] The Pacific hosts the two most active tropical cyclone basins, which are the northwestern Pacific and the eastern Pacific. Pacific hurricanes form south of Mexico, sometimes striking the western Mexican coast and occasionally the southwestern United States between June and October, while typhoons forming in the northwestern Pacific moving into southeast and east Asia from May to December. Tropical cyclones also form in the South Pacific basin, where they occasionally impact island nations.

In the arctic, icing from October to May can present a hazard for shipping while persistent fog occurs from June to December.[4] A climatological low in the Gulf of Alaska keeps the southern coast wet and mild during the winter months. The Westerlies and associated jet stream within the Mid-Latitudes can be particularly strong, especially in the Southern Hemisphere, due to the temperature difference between the tropics and Antarctica,[47] which records the coldest temperature readings on the planet. In the Southern hemisphere, because of the stormy and cloudy conditions associated with extratropical cyclones riding the jet stream, it is usual to refer to the Westerlies as the Roaring Forties, Furious Fifties and Shrieking Sixties according to the varying degrees of latitude.[48]

Geology

The ocean was first mapped by Abraham Ortelius; he called it Maris Pacifici following Ferdinand Magellan's description of it as "a pacific sea" during his circumnavigation from 1519 to 1522. To Magellan, it seemed much more calm (pacific) than the Atlantic.[49]

The dissimilarity continues northeastward along the western edge of the AndesCordillera along South America to Mexico, returning then to the islands off California. Indonesia, the Philippines, Japan, New Guinea, and New Zealand lie outside the andesite line.

Within the closed loop of the andesite line are most of the deep troughs, submerged volcanic mountains, and oceanic volcanic islands that characterize the Pacific basin. Here basaltic lavas gently flow out of rifts to build huge dome-shaped volcanic mountains whose eroded summits form island arcs, chains, and clusters. Outside the andesite line, volcanism is of the explosive type, and the Pacific Ring of Fire is the world's foremost belt of explosive volcanism.[28] The Ring of Fire is named after the several hundred active volcanoes that sit above the various subduction zones.

The Pacific Ocean is the only ocean which is almost totally bounded by subduction zones. Only the Antarctic and Australian coasts have no nearby subduction zones.

Geological history

The Pacific Ocean was born 750 million years ago at the breakup of Rodinia, although it is generally called the Panthalassic Ocean until the breakup of Pangea, about 200 million years ago.[8] The oldest Pacific Ocean floor is only around 180 Ma old, with older crust subducted by now.[54]

Fishing

Fish are an important economic asset in the Pacific. The shallower shoreline waters of the continents and the more temperate islands yield herring, salmon, sardines, snapper, swordfish, and tuna, as well as shellfish.[56] Overfishing has become a serious problem in some areas. For example, catches in the rich fishing grounds of the Okhotsk Sea off the Russian coast have been reduced by at least half since the 1990s as a result of overfishing.[95]

Environmental issues

The quantity of small plastic fragments floating in the north-east Pacific Ocean increased a hundredfold between 1972 and 2012.[13]

Marine pollution is a generic term for the harmful entry into the ocean of chemicals or particles. The main culprits are those using the rivers for disposing of their waste.[59] The rivers then empty into the ocean, often also bringing chemicals used as fertilizers in agriculture. The excess of oxygen-depleting chemicals in the water leads to hypoxia and the creation of a dead zone.

Marine debris, also known as marine litter, is human-created waste that has ended up floating in a lake, sea, ocean, or waterway. Oceanic debris tends to accumulate at the center of gyres and coastlines, frequently washing aground where it is known as beach litter.[59]

Universalis Cosmographia, the Waldseemüller map dated 1507, from a time when the nature of the Americas was ambiguous, particularly North America, as a possible part of Asia, was the first map to show the Americas separating two distinct oceans. South America was generally considered a "new world" and shows the name "America" for the first time, after Amerigo Vespucci

Made in 1529, the Diogo Ribeiro map was the first to show the Pacific at about its proper size

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Universalis Cosmographia, the Waldseemüller map dated 1507, from a time when the nature of the Americas was ambiguous, particularly North America, as a possible part of Asia, was the first map to show the Americas separating two distinct oceans. South America was generally considered a "new world" and shows the name "America" for the first time, after Amerigo Vespucci

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